But companies cannot assume they are operating more sustainably simply by moving to the cloud, some experts warn, because not all clouds are equally as clean.

Game theory

Markus Steinkamp, head of business intelligence for Berlin-based mobile games company Wooga, doesn't pretend sustainability issues were paramount in his company's decision to use cloud services.

"We wanted to outsource as much stuff as possible to leave our teams free to focus on games development rather than servers, " he says.

"The primary motivation was to lower costs; sustainability was a nice by-product."

Wooga, whose free games are played by about eight to 10 million people a day, uses Amazon Web Services to handle its games and Exasol as its main database provider.

"The cloud gives us the flexibility to respond to fluctuating market demand and only pay for the server capacity we need," says Mr Steinkamp.

Image copyrightWooga.comImage caption
Mobile games company Wooga.com relies on cloud services to run its operations as efficiently as possible

"Exasol's expertise in data compression gives better performance and reduces the number of servers we need, thus reducing energy consumption and cost," he adds.

Virtual computing, real savings

The logic of moving to the cloud is certainly compelling when you look at the numbers.

US cloud services provider Salesforce.com says that in 2012 its customers saved 587,628 tonnes of CO2 emissions by using cloud rather than on-site software.

We're shifting to a world where instead of moving Adams around, we're moving atomsPeter Coffee, Salesforce.com

This is equivalent to removing 122,000 cars from the road, it suggests.

"By moving to the cloud the carbon footprint reduction is about 95%," Peter Coffee, the company's vice-president of strategic research, told the BBC.

"Before, if you were preparing a document and collaborating with two or three colleagues, you'd each be using PCs, software and intermediate servers, resulting in thousands and thousands of watts of electricity being used.

"With the cloud model there's only one document in one place being accessed remotely. This represents a dramatic reduction in energy consumption."

Online collaboration also reduces the need for travel, a major contributor of global CO2 emissions, Mr Coffee argues.

"We're shifting to a world where instead of moving Adams around, we're moving atoms," he says.

Redundancy

By outsourcing hardware and software to the cloud, companies strip out redundancy, or unused capacity, from their IT systems, argues Kathrin Winkler, chief sustainability officer at global big data and cloud computing firm EMC.

Image copyrightAPImage caption
Companies like Apple, Google and Facebook aim to have all their data centres powered by renewable energy

"Most company servers are only being used at about 15% of their capacity," she says. "Some never get used at all."

Due to advances in server and database technology "what used to take 40 servers can now be done by one," she says.

Just moving to the cloud doesn't mean you're greener - a lot depends how efficiently the data centre is run and how its electricity is producedDuncan Ross, Teradata

By making the most of dynamically-managed, distributed computing that allows applications to be accessed from a range of different data centres simultaneously, companies can enjoy capacity on tap, argues Ms Winkler.

"As a result we've seen carbon savings of 10% to 40% through moving to the private or public cloud," she says.

Such improvements in efficiency mean Salesforce.com can service 140,000 businesses around the world with just 12,000 servers located in a handful of data centres, says Mr Coffee.

Guy Lipscombe, Exasol's UK and Ireland managing director, says: "The main ecological advantage of cloud computing is that resources are shared - it's similar to the fact that a train journey with 400 passengers is more efficient than those 400 passengers driving a single-occupant car."

Rising energy demand

But some fear that the explosion in the volume of digital data, caused largely by the growing number of networked mobile devices, internet transactions and sensor-equipped devices, is causing a proliferation of energy-hungry data centres.

"Energy demand in IT services will increase because of this growth in digital data," admits EMC's Ms Winkler.

This sounds alarming in the face of mounting evidence of a causal link between the burning of fossil fuels and climate change.

Image copyrightReutersImage caption
Do you know if your cloud provider's data centre is powered by a polluting coal-fired power station?

And industry contributes more than a quarter of global energy end use, the IPCC says.

This is putting pressure on internet companies to be more transparent about their carbon footprints and more innovative in reducing energy consumption.

But not all are succeeding.

Green data

Companies such as Apple, Box, Facebook, Google, Rackspace, and Salesforce.com, are all aiming to have their data centres powered by 100% renewable energy.

Amazon Web Services, on the other hand, is the "among the dirtiest and least transparent companies in the sector", environmental lobby group Greenpeace concludes in its April 2014 report, Clicking Clean.

"When you do stuff in the cloud, you don't necessarily know where the data centre is located or how it is powered - you can't guarantee the environmental credentials of the service provider," warns Duncan Ross, director of data science at Teradata, a data storage and analysis company.

Image copyrightGreen mountainImage caption
The Green Mountain data centre in Norway claims to be "the greenest in the world"

Andie Stephens, senior consultant the Carbon Trust, a business advisory body, agrees saying: "Just moving to the cloud doesn't mean you're greener - a lot depends how efficiently the data centre is run and how its electricity is produced.

"The geographic location of a data centre makes a 20% difference to how much energy it uses," he says. "About 60% of a data centre's energy use is spent on cooling.

An exemplar in the field is the award-winning Green Mountain data centre in Norway, which claims to be the greenest in the world.

Its energy comes from renewable hydro-electric power located nearby and the centre is sited underground in a former Nato ammunition store, thereby reducing cooling costs.

So if you want your business to operate more sustainably, you also need to know how clean is your cloud.